Selecting the right driver

**irving2008** · 05-09-2009

Originally Posted by Lee Roberts

So let’s take the PM542's (PDF), they have a Typical Supply Voltage of 36v with a MAX of 50v.

A late forum member told me I should supply them at the max (50v) is this the correct thing to do? Or would it be better to supply the driver with the Typical Rated Voltage?

I want to get the best speed I can from the motors, will supplying the driver at the MAX voltage mean the motor will also receive a higher voltage and give me better speeds?

If we take the Nema23 3Nm motor (PDF), the document said:

Bipolar Parallel 2.73v, 4.2a, 3Nm

So from that, i take it for the Motor to run at 3Nm Holding Torque it will require from the driver 2.73v and 4.2a ?

The other question i have is about the Motor, when a phase is "in use" is the Volts and Amps it is pulling from the driver divided by the amount of wires coming from the motor?

Lee, Gary has answered some of your points but let me throw in my 2p worth.

Electronic devices should never be run at the absolute maximum voltage quoted. Depending on the circuit this might either be the protective trip voltage or the voltage at which damage can occur due to internal breakdown of the device (which then results in high peak currents frying the device unless there is an external curent limit). In this instance its the protective trip. If you were to feed the driver with 50v there is the possibility that back-EMF from the motor when pushing energy back into the power supply (on the overrun/braking cycle) would cause the power supply voltage to rise and trip which would be inconvenient at best and catastrophic to the workpiece at worst! If your power supply is really good, with a regulation of better than 2% then you might get away with running it at 48v or so. But I'd stay below 45v on these drivers.

From the motor torque curves on Gary's site you can see that at 500steps/sec (150rpm) the torque is already down at 2Nm. Below 150rpm the torque will tend towards the holding torque but the relationship isn't linear. You will notice from these torque curves that the curve for 60v/4.3A is flatter/more linear than that for 40v/4.3A but the difference isnt really apparent below 2500steps/sec (750rpm). In other words if you are never going above 750rpm on the motor then 40v will perform as well as 60v. If you have only got 40v drivers then this information can be used to factor any gearing to keep the motor in the sweet spot.

The stepper driver is a constant current device. whatever the motor winding resistance the driver will never allow more than the rated current through the winding. For a driver set at 4.2A this is the maximum it will allow. The voltage rating of a stepper motor is irrelevant, it is merely the steady state voltage across the windings at the rated current due to the winding resistance. With a chopper or PWM current controller it has no meaning as the driver will switch the drive voltage on and off at high frequency to maintain the average current at the set value. Since it is being switched the winding inductance has a part to play as this controls the rate at which the current can change in the winding. This is where the higher voltage comes into play as a higher voltage can 'force' a higher current in a shorter time therefore maintaining the torque at higher speeds.

I'm guessing the meaning of your last question... refering to the data sheet for the motor again, when wired bipolar parallel the first phase has A and /C connected together and /A and C connected together. When that phase is energised, 4.2A of current flows from the driver along the connecting wire to the A + /C junction where it splits - 2.1A into each winding - and recombines at the /A + C junction, where 4.2A of current flows back to the driver. Therefore every one of the 4 wires connecting the driver to the motor carries 4.2A and needs to be rated for that.

Hope this helps...

**Lee Roberts** · 01-09-2009

Hi,

Well yea I know it would give error going over 50v, still need the questions answered please people.

Isn't the holdiong torque the same thing as "torque while moving" ?

**Gary** · 01-09-2009

Holding torues is at zero speed.
as soon as the motor starts to move the torque goes down.

Originally Posted by Lee Roberts

Hi,

Well yea I know it would give error going over 50v, still need the questions answered please people.

Isn't the holdiong torque the same thing as "torque while moving" ?

**paul.hunaban** · 27-03-2010

I've just purchased the stepper noted in #8 [ Nema23 3Nm motor (PDF), the document said: Bipolar Parallel 2.73v, 4.2a, 3Nm], connected to my existing driver and hey ho smoke all around.

I’m very interested to know, did you decide on a driver as I clearly need to upgrade what I had ?

**Lee Roberts** · 05-09-2009

Hi Irving, thanks for taking the time to go into details I appreciate it.

Now I don’t have one of the motors on the data sheet to hand, but I’m confident that this will be the same…

On the motors I have got here in front of me ( two different manufacturers ) the wire's coming from the motors is only 16/0.02, this motor is 4.2a in bipolar parallel setup.

I’ve looked at a few different websites selling the 16/0.02 equipment wire and they all seem to say that 16/0.02 wire is rated at 3a, if that is true then the wire on these motors is under rated for what the motor could potentially be doing ?

**irving2008** · 06-09-2009

Originally Posted by Lee Roberts

Hi Irving, thanks for taking the time to go into details I appreciate it.

Now I don’t have one of the motors on the data sheet to hand, but I’m confident that this will be the same…

On the motors I have got here in front of me ( two different manufacturers ) the wire's coming from the motors is only 16/0.02, this motor is 4.2a in bipolar parallel setup.

I’ve looked at a few different websites selling the 16/0.02 equipment wire and they all seem to say that 16/0.02 wire is rated at 3a, if that is true then the wire on these motors is under rated for what the motor could potentially be doing ?

Assuming an 8-wire motor, the motor wires only carry 2.1A, remember that the 4.2A is for bipolar parallel operation with 2 windings in use, 2.1A per winding. 16/0.2mm cable is rated for continuous 3A capacity. For the cables connecting to the driver, which are carryig 4.2A you should use 24/0.2mm which is rated at 6A continuous

**Lee Roberts** · 06-09-2009

Ahhh yes 2 windings ! Sorry !

Ok but if the cables connecting to the driver are carrying 4.2a, is that devided by 4 wires if the motor is in a bipolar parallel operation ?

Basicly Irving i just want to know what the correct rating of the wire should be that i use to connect the drivers to each motor/XLR. Can i not just use the same rated wire as whats on the motors or is it better to step down as you go?

**irving2008** · 06-09-2009

Originally Posted by Lee Roberts

Ahhh yes 2 windings ! Sorry !

Ok but if the cables connecting to the driver are carrying 4.2a, is that devided by 4 wires if the motor is in a bipolar parallel operation ?

Basicly Irving i just want to know what the correct rating of the wire should be that i use to connect the drivers to each motor/XLR. Can i not just use the same rated wire as whats on the motors or is it better to step down as you go?

Lee, the attached diagram might help.